Wireless communication systems and methods for long-code communications for regenerative multiple user detection involving implicit waveform subtraction

ABSTRACT

The invention provides improved CDMA, WCDMA (UTMS) or other spread spectrum communication systems of the type that processes one or more spread-spectrum waveforms, each representative of a waveform received from a respective user (or other transmitting device). The improvement is characterized by a first logic element that generates a residual composite spread-spectrum waveform as a function of an arithmetic difference between a composite spread-spectrum waveform for all users (or other transmitters) and an estimated spread-spectrum waveform for each user. It is further characterized by one or more second logic elements that generate, for at least a selected user (or other transmitter), a refined spread-spectrum waveform as a function of a sum of the residual composite spread-spectrum waveform and the estimated spread-spectrum waveform for that user.

BACKGROUND OF THE INVENTION

[0001] The invention pertains to wireless communications and, moreparticularly, to methods and apparatus for interference cancellation incode-division multiple access communications. The invention hasapplication, by way of non-limiting example, in improving the capacityof cellular phone base stations.

[0002] Code-division multiple access (CDMA) is used increasingly inwireless communications. It is a form of multiplexing communications,e.g., between cellular phones and base stations, based on distinctdigital codes in the communication signals. This can be contrasted withother wireless protocols, such as frequency-division multiple access andtime-division multiple access, in which multiplexing is based on the useof orthogonal frequency bands and orthogonal time-slots, respectively.

[0003] A limiting factor in CDMA communication and, particularly, inso-called direct sequence CDMA (DS-CDMA), is the interference betweenmultiple simultaneous communications, e.g., multiple cellular phoneusers in the same geographic area using their phones at the same time.This is referred to as multiple access interference (MAI). It has effectof limiting the capacity of cellular phone base stations, sinceinterference may exceed acceptable levels—driving service quality belowacceptable levels—when there are too many users.

[0004] A technique known as multi-user detection (MUD) reduces multipleaccess interference and, as a consequence, increases base stationcapacity. MUD can reduce interference not only between multiple signalsof like strength, but also that caused by users so close to the basestation as to otherwise overpower signals from other users (theso-called near/far problem). MUD generally functions on the principlethat signals from multiple simultaneous users can be jointly used toimprove detection of the signal from any single user. Many forms of MUDare known; surveys are provided in Moshavi, “Multi-User Detection forDS-CDMA Systems,” IEEE Communications Magazine (October, 1996) andDuel-Hallen et al, “Multiuser Detection for CDMA Systems,” IEEE PersonalCommunications (April 1995). Though a promising solution to increasingthe capacity of cellular phone base stations, MUD techniques aretypically so computationally intensive as to limit practicalapplication.

[0005] An object of this invention is to provide improved methods andapparatus for wireless communications. A related object is to providesuch methods and apparatus for multi-user detection or interferencecancellation in code-division multiple access communications.

[0006] A further object of the invention is to provide such methods andapparatus as can be cost-effectively implemented and as require minimalchanges in existing wireless communications infrastructure.

[0007] A still further object of the invention is to provide methods andapparatus for executing multi-user detection and related algorithms inreal-time.

[0008] A still further object of the invention is to provide suchmethods and apparatus as manage faults for high-availability.

SUMMARY OF THE INVENTION

[0009] These and other objects are met by the invention which provides,in one aspect, a wireless communications system, referred to as the“MCW-1” (among other terms) in the materials that follow, and methods ofoperation thereof. An overview of that system is provided in thedocument entitled “Software Architecture of the MCW-1 MUD Board,”immediately following this Summary. A more complete understanding of itsimplementation may be attained by reference to the other attachedmaterials.

[0010] In view of those materials, aspects of the invention include, butare not limited to, the following:

[0011] hardware and/or software architectures (and methods of operationthereof) for multi-user detection in wireless communications systems andparticularly, for example, in a wireless communications base station;

[0012] a hardware architecture (and methods of operation thereof) formulti-user detection in wireless communications systems pairing eachprocessing node with NVRAM and watchdog PLD for fault management;

[0013] methods and apparatus for connecting watchdog PLDs with anout-of-band fault-management bus;

[0014] methods and apparatus for use of an embedded host with theRACEway™ architecture of Mercury Computer Systems, Inc.

[0015] methods and apparatus for interfacing a digital signal processorto the RACEway™ architecture;

[0016] methods and apparatus for interfacing the RACEway™ architectureto a programming port in a device for multi-user detection in wirelesscommunications systems;

[0017] methods and apparatus for implementing a DMA Engine FPGA for usein multi-user detection in a wireless communications systems;

[0018] methods and apparatus for implementing a hardware-based resetvoter and stop voter;

[0019] methods and apparatus for scalable mapping of handset and BTSfunctions to multiple processors;

[0020] methods and apparatus for facilitating allocation and managementof buffers for interconnecting processors that implement theaforementioned mapping;

[0021] methods and apparatus for implementing a hybrid operating system,e.g., with the VxWorks operating system (of WindRiver Systems, Inc.) ona host computer and the MC/OS operating system on RACE®-based nodes.(Race and MC/OS are trademarks of Mercury Computer Systems, Inc.);

[0022] methods and apparatus for high-availability multi-user detectionin wireless communications systems, including (by way of non-limitingexample) round-robin fault testing and use of NVRAM to store faultsymptoms and use of master to diagnose faults from NVRAM contents;

[0023] class library-based methods and apparatus for facilitatinginterprocessor communications, by way of non-limiting example, inbuffering for multi-user detection in wireless communications systems;

[0024] methods and apparatus for implementation of R-matrix,gamma-matrix and MPIC computations on separate processors in a devicefor multi-user detection in wireless communications systems;

[0025] methods and apparatus for computing complementary R-matrixelements in parallel using multiple processors in a device formulti-user detection in wireless communications systems;

[0026] methods and apparatus for depositing results of R-matrixcalculations contiguously in memory in a device for multi-user detectionin wireless communications systems;

[0027] methods and apparatus for increasing the number of MPIC andR-matrix calculations performed in cache in a device for multi-userdetection in wireless communications systems;

[0028] methods and apparatus for performing a gamma-matrix calculationin FPGA in a device for multi-user detection in wireless communicationssystems;

[0029] methods and apparatus for equalizing load of R-matrix-elementcalculation among multiple processors in a device for multi-userdetection in wireless communications systems; and

[0030] methods and apparatus for use of Altivec registers andinstruction set in performing MUD calculations in a wirelesscommunications system.

[0031] These and other aspects of the invention (including utilizationof the aforementioned methods and aspects for other than wirelesscommunications and/or interference cancellation) are evident in thematerials that follow.

[0032] departing from the scope of the present invention. For example,multiple summations can be utilized by a system of the invention, andnot separate summations as described herein. More-over, by way offurther non-limiting example, it will be appreciated that although theterminology used above is largely based on the UMTS CDMA protocols, thatthe methods and apparatus described herein are equally applicable toDS/CDMA, CDMA2000 1X, CDMA2000 1xEV-DO, and other forms of CDMA.

Therefore, in view of the foregoing, what we claim is:
 1. In a spreadspectrum communication system of the type that processes one or morespread-spectrum waveforms (“user spread-spectrum waveforms”), eachrepresentative of a waveform associated with a respective user, theimprovement comprising: a first logic element that generates a residualcomposite spread-spectrum waveform as a function of a compositespread-spectrum waveform and an estimated composite spread-spectrumwaveform, one or more second logic elements each coupled to the firstlogic element, each second logic element generating a refinedmatched-filter detection statistic for at least a selected user as afunction of (i) the residual composite spread-spectrum waveform and (ii)a characteristic of an estimate of the selected user's spread-spectrumwaveform.
 2. In the system of claim 1, the further improvement whereinthe characteristic is at least one of an estimated amplitude and anestimated symbol associated with the estimate of the selected user'sspread-spectrum waveform.
 3. In the system of claim 1, the improvementwherein the spread-spectrum communications system comprises a codedivision multiple access (CDMA) base station.
 4. In the system of claim1, the improvement wherein the CDMA base station comprises one or morelong-code receivers, and each long-code receiver generating one or morerespective matched-filter detection statistics, from which the estimatedcomposite spread-spectrum waveform is, in part, generated.
 5. In thesystem of claim 1, the improvement wherein the first logic elementcomprises summation logic which generates the residual compositespread-spectrum waveform based on the relationr_(res)^((n))[t] ≡ r[t] − r̂^((n))[t],

wherein r_(res)^((n))[t]

is the residual composite spread-spectrum waveform, r[t] represents thecomposite spread-spectrum waveform, {circumflex over (r)}^((n))[t]represents the estimated composite spread-spectrum waveform, t is asample time period, and n is an iteration count.
 6. In the system ofclaim 5, the further improvement wherein the estimated compositespread-spectrum waveform is pulse-shaped and is based on estimatedcomplex amplitudes, estimated delay lags, estimated symbols, and codesof the one or more user spread-spectrum waveforms.
 7. In the system ofclaim 1, the further improvement wherein each second logic elementcomprises rake logic and summation logic which generates the refinedmatched-filter detection statistics based on the relationy_(k)^((n + 1))[m] = A_(k)^((n)²) ⋅ b̂_(k)^((n))[m] + y_(res, k)^((n))[m]

wherein A_(k)^((n)²)

represents an amplitude statistic, b̂_(k)^((n))[m]

represents a soft symbol estimate for the k^(th) user for the m^(th)symbol period, y_(res, k)^((n))[m]

represents a residual matched-filter detection statistic for the k^(th)user, and n is an iteration count.
 8. In the system of claim 1, thefurther improvement wherein the refined matched-filter detectionstatistic for each user is iteratively generated.
 9. In the system ofclaim 1, the further improvement wherein the refined matched-filterdetection statistic for at least a selected user is generated by along-code receiver.
 10. In the system of claim 1, the improvementwherein the first and second logic elements are implemented on any ofprocessors, field programmable gate arrays, array processors andco-processors, or any combination thereof.
 11. In a spread spectrumcommunication system of the type that processes one or more userspread-spectrum waveforms, each representative of a waveform associatedwith a respective user, the improvement comprising: a first logicelement which generates an estimated composite spread-spectrum waveformthat is a function of estimated user complex channel amplitudes, timelags, and user codes, a second logic element coupled to the first logicelement, the second logic element generating a residual compositespread-spectrum waveform a function of a composite user spread-spectrumwaveform and the estimated composite spread-spectrum waveform, one ormore third logic elements each coupled to the second logic element, thethird logic element generating a refined matched-filter detectionstatistic for at least a selected user as a function of (i) the residualcomposite spread-spectrum waveform and (ii) a characteristic of anestimate of the selected user's spread-spectrum waveform.
 12. In thesystem of claim 11, the further improvement wherein the characteristicis at least one of an estimated amplitude, an estimated delay lag and anestimated symbol associated with the estimate of the selected user'sspread-spectrum waveform.
 13. In the system of claim 11, the improvementwherein the spread-spectrum communications system is a code divisionmultiple access (CDMA) base station.
 14. In the system of claim 13, theimprovement wherein the CDMA base station comprises long-code receivers.15. In the system of claim 11, the improvement wherein the first logicelement further comprises arithmetic logic which generates the estimatedcomposite spread-spectrum waveform based on the relation${{{\hat{r}}^{(n)}\lbrack t\rbrack} = {\sum\limits_{r}{{g\lbrack r\rbrack}{\rho^{(n)}\left\lbrack {t - r} \right\rbrack}}}},$

wherein {circumflex over (r)}^((n))[t] represents the estimatedcomposite spread-spectrum waveform, g[t] represents a raised-cosinepulse shape.
 16. In the system of claim 15, the further improvementwherein the first logic element comprises arithmetic logic whichgenerates an estimated composite re-spread waveform based on therelation${{\rho^{(n)}\lbrack t\rbrack} = {\sum\limits_{k = 1}^{K_{v}}\quad {\sum\limits_{p = 1}^{L}\quad {\sum\limits_{r}\quad {{\delta \left\lbrack {t - {\hat{\tau}}_{kp}^{(n)} - {rN}_{c}} \right\rbrack} \cdot {\hat{a}}_{kp}^{(n)} \cdot {c_{k}\lbrack r\rbrack} \cdot {{\hat{b}}_{k}^{(n)}\left\lbrack \left\lfloor {r/N_{k}} \right\rfloor \right\rbrack}}}}}},$

wherein K_(v) is a number of simultaneous dedicated physical channelsfor all users, δ[t] is a discrete-time delta function, â_(k  p)^((n))

is an estimated complex channel amplitude for the p^(th) multipathcomponent for the k^(th) user, C_(k)[r] represents a user codecomprising at least a scrambling code, an orthogonal variable spreadingfactor code, and a j factor associated with even numbered dedicatedphysical channels, b̂_(k)^((n))[m]

represents a soft symbol estimate for the k^(th) user for the m^(th)symbol period, τ̂_(k  p)^((n))

is an estimated time lag for the p^(th)th multipath component for thek^(th) user, N_(k) is a spreading factor for the k^(th) user, t is asample time index, L is a number of multi-path components., N_(c) is anumber of samples per chip, and n is an iteration count.
 17. In thesystem of claim 11, the improvement wherein the second logic elementcomprises summation logic which generates the residual compositespread-spectrum waveform that based on the relationr_(res)^((n))[t] ≡ r[t] − r̂^((n))[t],

wherein r_(res)^((n))[t]

is the residual composite spread-spectrum waveform, r[t] represents thecomposite spread-spectrum waveform, {circumflex over (r)}^((n))[t]represents the estimated composite spread-spectrum waveform, t is asample time period, and n is an iteration count.
 18. In the system ofclaim 17, the further improvement wherein the estimated compositespread-spectrum waveform is pulse-shaped and is based on the userspread-spectrum waveform.
 19. In the system of claim 18, the furtherimprovement wherein each third logic element comprises rake logic andsummation logic which generates the second user matched-filter detectionstatistic based on the relationy_(k)^((n + 1))[m] = A_(k)^((n)²) ⋅ b̂_(k)^((n))[m] + y_(res, k)^((n))[m],

wherein A_(k)^((n)²)

represents an amplitude statistic, b̂_(k)^((n))[m]

represents a soft symbol estimate for the k^(th) user for the m^(th)symbol period, y_(res, k)^((n))[m]

represents the user residual matched-filter detection statistic for them^(th) symbol period, and n is an iteration count.
 20. In the system ofclaim 11, the further improvement wherein the refined matched-filterdetection statistic for each user is iteratively generated.
 21. In thesystem of claim 11, the improvement wherein the logic elements areimplemented on any of a processors, field programmable gate arrays,array processors and co-processors, or any combination thereof.
 22. Amethod for multiple user detection in a spread-spectrum communicationsystem that processes long-code spread-spectrum user transmittedwaveforms comprising: generating a residual composite spread-spectrumwaveform as a function of an arithmetic difference between a compositespread-spectrum waveform and an estimated spread-spectrum waveform,generating a refined matched-filter detection statistic that is afunction of a sum of a rake-processed residual composite spread-spectrumwaveform for a selected user and an amplitude statistic for thatselected user.
 23. The method of claim 22, comprising generating arefined matched-filter detection statistic that is a function of a sumof a rake-processed residual composite spread-spectrum waveform for aselected user and an amplitude statistic for that selected usermultiplied by a soft symbol estimate.
 24. The method of claim 22,further wherein the spread-spectrum communications system is a codedivision multiple access (CDMA) base station.
 25. The method of claim22, wherein the step of generating the residual compositespread-spectrum waveform further comprises performing arithmetic logicthat is based on the relation r_(res)^((n))[t] ≡ r[t] − r̂^((n))[t],

wherein r_(res)^((n))[t]

is the residual composite spread-spectrum waveform, r[t] represents thecomposite spread-spectrum waveform, {circumflex over (r)}^((n))[t]represents the estimated composite spread-spectrum waveform, t is asample time period, and n is an iteration count.
 26. The method of claim22, wherein the estimated composite spread-spectrum waveform ispulse-shaped and is based on a composite user re-spread waveform. 27.The method of claim 22, wherein the step of generating the refinedmatched-filter detection statistic representative of that user furthercomprises performing arithmetic logic based on the relationy_(k)^((n + 1))[m] = A_(k)^((n)²) ⋅ b̂_(k)^((n))[m] + y_(res, k)^((n))[m]

wherein b̂_(k)^((n))[m]

represents an amplitude statistic, b̂_(k)^((n))[m]

represents a soft symbol estimate for the k^(th) user for the m^(th)symbol period, y_(res, k)^((n))[m]

represents a residual matched-filter detection statistic, and n is aniteration count.
 28. The method of claim 22, the further improvementwherein the refined matched-filter detection statistic is generated by along-code receiver.
 29. The method of claim 22, the further improvementwherein the step of generating the residual matched-filter detectionstatistic for an m^(th) symbol period comprises performing arithmeticlogic based on the relation${y_{{res},k}^{(n)}\lbrack m\rbrack} \equiv {{Re}\left\{ {\sum\limits_{p = 1}^{L}{{{\hat{a}}_{kp}^{{(n)}H} \cdot \frac{1}{2N_{k}}}{\sum\limits_{r = 0}^{N_{\lambda} - 1}{{r_{res}^{(n)}\left\lbrack {{rN}_{c} + {\hat{\tau}}_{kp}^{(n)} + {mT}_{k}} \right\rbrack} \cdot {c_{km}^{*}\lbrack r\rbrack}}}}} \right\}}$

wherein y_(res, k)^((n))[m]

represents the user residual matched-filter detection statistic for them^(th) symbol period, L is a number of multi-path components,â_(kp)^((n))

is the estimated complex channel amplitude for the p^(th) multipathcomponent for the k^(th) user, N_(k) is the spreading factor for thek^(th) user, r_(res)^((n))[t]

is the residual composite spread-spectrum waveform, N_(c) is the numberof samples per chip, and τ̂_(kp)^((n))

is the time lag for the p^(th) multipath component for the k^(th) user,m is a symbol period, T_(k) is a channel symbol duration for the k^(th)user, C_(km)[r] represents a user code comprising at least a scramblingcode, an orthogonal variable spreading factor code, and a j factorassociated with even numbered dedicated physical channels. n is aniteration count.